Process for bonding metals by explosive means



July 14, 1964 H. HOLTZMAN 3,140,539

PROCESS FOR BONDING METALS BY EXPLOSIVE MEANS Filed June 28, 1962 FIG?) ATTORNEY United States Patent 3,140,539 PROCESS FOR BONDING METALS BY EXPLOSIVE MEANS Arnold Harold Holtzman, Cherry Hill Township, N.J., assignor to E. I. du Pont de Nemours and Company,

Wilmington, DeL, a corporation of Delaware Filed June 28, 1962, Ser. No. 206,066

6 Claims. (Cl. 29-497.5)

The present invention relates to an improved method for bonding metals by explosive means.

A process has been described recently for bonding metal layers to form a multilayered body. In general this is accomplished by supporting one metal layer a distance of at least 0.001 inch from a second metal layer, placing a layer of an explosive having a detonation velocity less than 120% of the sonic velocity of the metal in the system with the highest sonic velocity on the outside surface of one of the metal layers, and initiating the explosive so that detonation is propagated parallel to the metal layers.

Although the bonding obtained by this process is excellent, occasionally areas contiguous to the point of initiation of the explosive layer are left unbonded. This problem is frequently encountered when the explosive is initiated by means of a blasting cap, detonating cord, or some other device positioned approximately in the center of the layer in which case the unbonded zone extends over an essentially circular area in the center of the interface between the two metal layers.

We have found that this difiiculty is overcome by (1) providing a convex projection having a radius of curvature of at least about 0.25 inch on one surface in the plane of a first metal layer, (.2) supporting said first metal layer parallel to and coextensive with a second metal layer so that said convex projection faces the second metal layer and the inner, flat surfaces of the two metal layers are separated by a distance of at least 0.010 inch, the height of said convex projection being no greater than the distance between the inner fiat surfaces of the two metal layers, (3) placing a layer of a detonating explosive having a velocity of detonation less than 100% of the sonic velocity of the metal in the system having the highest sonic velocity on the outside surface of one of the metal layers, parallel to and coextensive with the surfaces to be bonded, and (4) initiating the explosive at a point in the explosive layer contiguous to said convex projection of the first metal layer and Within the area in the explosive layer which corresponds to the area of the base of the convex projection. v

The term cladding layer as used hereinafter refers to that metal layer upon which the explosive is placed and the term base layer refers to the metal layer toward which the cladding layer is propelled by the explosive pressure, i.e., the surfaces of the cladding and base layers are the surfaces to be bonded. In commercial practice the base layer will often be a specific area on the surface of an implement or unit of equipment. For example, the base layer can be that area of a reactor to which a cladding patch is to be atfixed.

For a more complete understanding of the invention reference is now made to the drawings in which like numbers indicate similar elements and in which FIGURE 1 illustrates a portion of the cross-section of an assembly which may be used for the practice of the present invention,

FIGURE 2 represents a top view of a portion of an assembly which may be used for the practice of the present invention, and

FIGURE 3 represents a top view of a portion of another assembly which may be used for the practice of the present invention.

layers, the loading and confinement of the explosive layer,

and the particular device(s) used to initiate the explosive layer are not critical. The convex projection in the metal layer may be simply a small lump of metal welded or otherwise attached to the surface of the layer, or it may be a concave-convex dimple as shown in FIGURE 1. The explosive cladding process wherein the convex projection is the latter represents a preferred embodiment of the present invention. The dimple may be made by a number of methods which are obvious to one skilled in the art. For example, the dimple may be provided by hydraulically pressing a steel ball against the metal layer as is more fully described hereinafter.

Effective bonding will not be obtained if the metal cladding layer, i.e., the metal layer upon which the layer of explosive is placed, is propelled in gross against the second or metal base layer by travelling in a direction generally normal to the surface of the metal base layer. In other words, the two metal layers must make contact at an angle in order to insure formation and/or effective circulation of the jet which is responsible for the formation of the bond between the layers.

Although we do not intend to be limited by any theory of operation we believe that in some cases in which no bond is produced between the metal layers contiguous to the point of initiation of the explosive layer, that portion of the metal cladding layer was propelled in gross against the metal base layer over an area of sufficient size to prevent formation and/ or effective circulation of the jet between the layers and thus an unbonded Zone adjacent to the point of initiation of the explosive remains. The process of the present invention in which a convex projection is provided in one of the metal layers provides an angle between the metal layers adjacent to the point of initiation of the explosive and thus results in a completely and uniformly, metallurgically bonded clad metal system.

The minimum separation or standoff between the parallel metal cladding and base layers which will result in effective bonding is about 0.001 inch. The optimum size of this standoff depends upon a number of factors including metal cladding layer composition and thickness, explosive composition, loading, and confinement, etc. In most cases a standoff of 0.0 10 inch or more is desirable. The method of maintaining this standoff between the inner, flat surfaces of the metal layers is not critical. The cladding layer is readily supported by thin metal ribbons which are corrugated, i.e., deformed in a sine wave con-- figuration normal :to their thickness, and placed on edge on the base layer as illustrated in FIGURES 2 and 3. Metal ribbons in a variety of configurations, e.g., twisted along their longitudinal axes, also are satisfactory.

We have found that when a standoff between about 0.010 and 0.030 inch is used in the process of the present invention, a convex projection of a height equal to the desired standoff is preferable. For ease of handling the first metal layer can be secured to the second metal layer, for example, by means of a spot weld at the point of contact between the convex projection and the second metal layer.

Further, we have found that in cases in which a standoff of more than about 0.030 inch is desired, the present invention is practiced most conveniently by providing a metal layer with a convex projection having a height of about five-sixths of the desired standoff.

The area of the base of the convex projection must be larger than that of the portion of the explosive layer which is essentially immediately initiated by the action of the initiating device. In other words, if the explosive layer is initiated, for example, by means of a low energy detonating cord inch in diameter, the base of the convex projection must have a diameter greater than A inch (see FIGURE 1). Further, the location of the point (or area) of initiation of the explosive layer must be contiguous to the convex projection and within the area in the explosive layer which corresponds to the area of the base of the projection, for example, as illustrated in FIG- URE 1. This position generally will be approximately in the center of the layer.

The size of the base of the projection is determined by the height and the radius of curvature of the projection. The optimum radius of projection depends, among other things, upon the formability of the metal layer. As is obvious to one skilled in the art, all other conditions being equal, a dimple having a smaller radius of curvature can be made in a thin, ductile metal layer than can be made in a thick, less ductile metal layer. We have found that the optimum radius of curvature of the convex projection is generally at least about Mi inch.

The following examples illustrate some of the modifications of the process of the present invention. They are intended as illustrative only, however, and are not to be considered as exhaustive or limiting.

Example 1 An assembly having a cross-section substantially as illustrated schematically in FIGURE 1 was prepared as follows:

A dimple .100 inch deep and having a radius of curvature of inch was made in the center of a copper plate A inch thick, 12 inches wide, and 12 inches long by hydraulically pressing a steel ball 4 inch in diameter against the center of the plate. The copper plate was placed on top of and parallel to a mild steel plate inch thick, 12 inches wide and 12 inches long so that the center of the convex surface of the dimple was .020 inch above the center of the mild steel plate. The adjacent flat surfaces of the two plates were separated by a distance of .120 inch maintained by 20 mild steel ribbons which were spot Welded on the upper surface of the mild steel plate substantially as illustrated in FIGURE 2. Each of these ribbons was .002 inch thick and .120 inch wide and was bent normal to its longitudinal axis into a sine wave configuration of 3 cycles per linear inch and approximately .050 inch amplitude. Each ribbon was set on edge" on the mild steel plate, i.e., so that the .120 inch dimension of the ribbon was perpendicular to the plane of the plate. The upper surface of the copper plate was covered with a layer of a grained amatol explosive comprising 80 parts ammonium nitrate and 20 parts trinitrotoluene. The layer of explosive, which was contained in a wooden frame A; inch thick and about 1% inches high placed on the perimeter of the copper plate was about 1.25 inches thick. (The thickness of the explosive layer increased from 1.25 to 1.35 inches over the circular area which corresponded to the indentation in the center of the copper plate.) The explosive had a weight distribution of about 16.55 grams per square inch and a detonation velocity of about 4,000 meters per second. A cord .178 inch in diameter and 2 inches long of an explosive comprising 24 parts very fine pentaerythritol tetranitrate, 67 parts red lead, 2.36 parts polybutene, 2.25 parts refined mineral oil, 1.69 parts polyisobutylene, 1.35 parts butyl rubber, and 1.35 parts of an aromatic hydrocarbon resin plasticizer and having a detonation velocity of about 4370 meters per second was positioned in the center of the layer of amatol explosive. An electric blasting cap having lead wires to a source of electric current was attached to the .4 free end of the explosive cord to form an assembly the center portion of the cross-section of which is illustrated schematically in FIGURE 1. The layer of amatol explosive was covered with waxed paper and the entire assembly was covered with a pile of sand 3 feet deep.

The blasting cap was actuated by application of electric current and initiated, in turn, the explosive cord and the layer of amatol explosive. After detonation, the copper and mild steel were found to be uniformly, metallurgically bonded together. Ultrasonic probing revealed no unbonded zones or discontinuities in the center of the composite system.

A ,second clad metal system of the composition and dimensions described above was prepared using the technique described above. However, no dimple was made in the center of the copper plate and the two plates were separated a distance of .120 inch over the entire areas of their adjacent surfaces. A uniform layer of explosive 1.25 inches thick was used. After detonation it was found by ultrasonic probing that no bond existed between the copper and the mild steel plates over a substantially circular area 2 inches in diameter in the center of the interface between the two plates.

Example 2 A copper-on-mild steel clad metal system was prepared using the technique described in Example 1. In this example the copper plate was inch thick, 12 inches wide, and 24 inches long. A dimple was made in the center of the plate as described in Example 1. The mild steel plate was inch thick, 12 inches wide, and 24 inches long. After detonation, ultrasonic probing revealed no discontinuity in the center of the metallurgically bonded system beneath the point of initiation of the explosive layer.

A second copper-on-mild steel composite of the dimensions given above in this example was prepared using the technique described in Example 1. However, no dimple was made in the center of the copper plate and after detonation it was found by ultrasonic probing that no bond existed between the copper and mild steel plates over a substantially circular area approximately 2 inches in diameter in the center of the interface between the two plates.

Example 3 A dimple .015 inch deep and having a radius of curvature of inch was made in the center of a copper plate .020 inch thick, 4 inches wide, and 6 inches long as described in Example 1. The copper plate was placed on top of and parallel to a mild steel plate /2 inch thick, 4 inches wide, and 6 inches long so that the center of the convex surface of the dimple rested on the center of the mild steel plate. The adjacent fiat surfaces of the two plates were separated by a distance of .015 inch maintained by 6 iron ribbons which were spot welded on the upper surface of the mild steel plate substantially as illustrated in FIGURE 3. Each of these ribbons was .001 inch thick and .015 inch wide and was bent normal to its longitudinal axis into a sine wave configuration of 20 cycles per linear inch and approximately .020 inch amplitude. Each ribbon was set on edge on the mild steel plate, i.e., so that the .015 inch dimension of the ribbon was perpendicular to the plane of the plate. The copper and mild steel plates were spot welded together at the point of contact between the convex surface of the dimple in the copper plate and the center of the mild steel plate. The upper surface of the copper plate was covered with a layer of a grained amatol explosive comprising 50 parts ammonium nitrate and 50 parts trinitrotoluene. The layer of explosive, which was contained in a wooden frame /a inch thick and about inch high placed on the perimeter of the copper plate, was about .375 inch thick. (The thickness of the explosive layer increased from .375 inch to .38 inch over the circular area which corresponded to the indentation in the center of the copper plate.) The explosive had a Weight distribution of about 5.35

grams per square inch and a detonation velocity of about 3500 meters per second. An explosive cord and an electric blasting cap were attached to the center of the layer of explosive as described in Example 1. The explosive was initiated as in Example 1. However, in this example detonation was carried out in air rather than under sand confinement. After detonation, the copper and mild steel were found to be uniformly, metallurgically bonded together. Ultrasonic probing and metallographic examination revealed no unbonded zones or discontinuities in the center of the composite system.

Example 4 A copper-on-mild steel composite system 4 inches wide and 6 inches long was made using a modification of the technique described in Example 3. In this example, the copper plate was .050 inch thick and a dimple .020 inch deep was made in the center of the plate as described in Example 1. A spacing of .020 inch was provided between the adjacent flat surfaces of the copper and mild steel plates by shim steel cups .002 inch thick and .020 inch deep one of which was spot welded in each of the corners of the upper surface of the mild steel plate. The copper and mild steel plates were spot welded together at the point of contact between the center of the convex surface of the dimple in the copper plate and the center of the mild steel plate. The cladding process was carried out as in Example 3. After detonation, ultrasonic probing and metallurgical examination revealed no discontinuity in the center of the metallurgically bonded system beneath the point of initiation of the explosive layer.

The invention having been fully described in the foregoing we intend to be limited only by the following claims.

I claim:

1. A process for producing a completely bonded clad metal system which comprises:

(a) providing a convex projection having a radius of curvature of at least about .25 inch on one surface in the plane of a first metal layer,

(b) supporting said first metal layer parallel to and coextensive with a second metal layer so that the convex projection in the first metal layer faces the second metal layer and the inner, substantially flat surfaces of the two metal layers are separated by a distance of at least 0.010 inch, the height of said convex projection being no greater than the distance between said inner flat surfaces of the two metal layers,

(0) placing a layer of a detonating explosive having a velocity of detonation less than 100% of the sonic velocity of the metal in the system having the highest sonic velocity on the outside surface of one of the metal layers, and

(d) initiating the explosive layer at a point in said explosive layer contiguous to said convex projection of the first metal layer.

2. A process as in claim 1 wherein the height of said convex projection is equal to said distance between the inner, flat surfaces of said metal layers.

3. A process as in claim 1 wherein the height of said convex projection is less than said distance between the inner, fiat surfaces of said metal layers.

4. A process as in claim 1 wherein the height of said convex projection and said distance between the inner, flat surfaces of said metal layers are equal and are no less than 0.010 inch and no more than 0.030 inch.

5. A process as in claim 1 wherein the height of said convex projection is less than said distance between the inner, flat surfaces of said metal layers and wherein said distance between the inner, flat surfaces of said metal layers is more than 0.030 inch.

6. A process as in claim 1 wherein said convex projection comprises the convex side of a concave-convex dimple in the metal layer.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A PROCESS FOR PRODUCING A COMPLETELY BONDED CLAD METAL SYSTEM WHICH COMPRISES: (A) PROVIDING A CONVEX PROJECTION HAVING A RADIUS OF CURVATURE OF AT LEAST ABOUT .25 INCH ON ONE SURFACE IN THE PLANE OF A FIRST METAL LAYER, (B) SUPPORTING SAID FIRST METAL LAYER PARALLEL TO AND COEXTENSIVE WITH A SECOND METAL LAYER SO THAT THE CONVEX PROJECTION IN THE FIRST METAL LAYER FACES THE SECOND METAL LAYER AND THE INNER, SUBSTANTIALLY FLAT SURFACES OF THE TWO METAL LAYERS ARE SEPARATED BY A DISTANCE OF AT LEAST 0.010 INCH, THE HEIGHT OF SAID CONVEX PROJECTION SAID INNER FLAT SURFACES OF THE TWO METAL LAYERS, (C) PLACING A LAYER OF A DETONATING EXPLOSIVE HAVING A VELOCITY OF DETONATION LESS THAN 100% OF THE SONIC VELOCITY OF THE METAL IN THE SYSTEM HAVING THE HIGHEST SONIC VELOCITY ON THE OUTSIDE SURFACE OF ONE OF THE METAL LAYERS, AND 